1. The Field of the Invention
This invention concerns a laboratory centrifuge having a rotor chamber which can be closed by a casing cover and a housing which contains a motor-driven vertical-axis rotor to accept test tubes and which, during operation, has cooling air flowing through the housing upward into the rotor chamber.
2. The Relevant Technology
Laboratory centrifuges are well known. An exemplary laboratory centrifuge is provided, for example, in EP 0 455 876 A2. The laboratory centrifuge disclosed is arranged in a housing and has a motor driving a vertically oriented drive shaft. The test tubes, which are warmed by friction during operation of the centrifuge, are cooled by forced-air cooling which sucks in air in the direction of the axis of the shaft. In order to create a simple and economical air-cooled centrifuge in which it is certain that the cooling air neither carries suspended matter into the samples nor carries suspended matter out of the rotor housing, even if a test tube should break, the rotor is surrounded by an air-tight container. A fan wheel is set on the driven end of the shaft and air is sucked through openings in the floor surface of the housing below the fan wheel into the housing to be guided along upward to the walls of the air-tight container and to be axially distributed through operation of the fan wheel.
A centrifuge is also known from German patent DE 39 13 792 A1 in which noise from empty test tube holders is suppressed. The centrifuge is a conventional centrifuge having a rotor with a plurality of holders to accept test tubes set in the rotor in a circular configuration. The whistling noise produced by empty holders is suppressed by a flexible flap which has a fixed or stationary end attached to the rotor by an adapter and a free end lying opposite. In the non-rotating or non-operative state of the rotor, the free end extends radially inward in the direction toward the center of the rotor. In the rotating state of the rotor, the free end becomes folded over or backwards by the centrifugal force in such a way that it covers the opening of the empty test tube holder(s). Thus, the covering of the opening(s) by the flexible flap prevents the occurrence of the undesired high-pitched shrill whistling noise which would otherwise be produced by the holder if it is rotating without a test tube set in it.
A laboratory centrifuge is also known from DD 265 754 A3 which provides for air guided in a casing cover to cool the rotor. The centrifuge rotor sweeps away the air located in the rotor chamber and throws it outward. The air put under pressure in this manner is pressed through an opening located in the annular gap between the rotor and the rotor chamber and, thus, into an exit channel to be guided out to the surrounding atmosphere. The negative pressure formed in the rotor chamber is equalized by supplying air through an air entry channel also arranged in the area of the casing cover. This design requires a specially manufactured casing cover and, thus, increases the cost of the centrifuge.
A problem with air cooling of centrifuges is that, particularly in the area above the rotor, the air is very turbulent and produces significant noise. It would be an advance to provide a laboratory centrifuge that permitted air to flow around the rotor at flow rates which produce sufficient cooling yet demonstrated low turbulence and low noise.